I only know about cephalopods, but the mechanism of the chromatophores is basically one of manipulating vesicle size, location, and distribution - it isn't something that would evolve in many many lines, but as an mutational variant - first simple shades, then patterns, then finer control from the nervous systems - it doesn't seem unexplainable. I don't think anyone had really looked at the systems from an evolutionary-development slant, though.

That's a really good question Gloone, cephalopods is biolumination a chemical process i don't know to much about it really but it has always fascinated me.

All i understand is with chromatophores they are single cells that contain pigments which are controlled by signals sent by the reptiles brain and there are billions of them they can switch on or off and change to various parts of the body.

As with the evolution of this process through natural selection all i can think of once again are the basics where we have a group of reptiles and like any evolutionary adaptation it has taken millions of years to evolve so early crude variations of chromatophores kicked off maybe only being able to change to one color those that did not inherit the gene of being able too died off those that did flourished.

As time went by that may of changed to being able to change to two or three different colors as the chromatophores evolved and become more advanced those (if any left) that could only produce a single color died off as a likely scenario would be say the organism needing to change from a dark green to say a brown which plays an important role in their survival with the environment they are livin in, those that could only produce say a yellow vanished as it was nowhere near any of the colors in the environment it was living in at the time.

And of course as time went by the chromatophores are highly efficient modern day not only being able to change to solid colors but also many variations of that color probably becoming to an evolutionary dead end as i don't think chromatophores could get any better, as they say ya cant improve on the already perfect!!

Anyway hopefully that lot above is of some help i am hopeless at explaining things.

Its also possible that the chromatophores evolved from some primitive proto-chromatophore that had nothing to do with camoflage. To varying degrees, humans have melanin which darkens on exposure to the sun to prevent UV damage. On the downside, melanin can interfere with vitamin D production which needs UV. I have no idea whether chameleons produce their own vitamin D, but maybe they needed to respond more quickly to intense sun and shade, and these cells eventually came to be used for camoflage purposes.

Rap wrote:Its also possible that the chromatophores evolved from some primitive proto-chromatophore that had nothing to do with camoflage. To varying degrees, humans have melanin which darkens on exposure to the sun to prevent UV damage. On the downside, melanin can interfere with vitamin D production which needs UV. I have no idea whether chameleons produce their own vitamin D, but maybe they needed to respond more quickly to intense sun and shade, and these cells eventually came to be used for camoflage purposes.